It is known in the art for a surgeon to utilize slice images of a patient's internal organs to plan a course of a medical procedure, be it diagnostic, therapeutic or surgical. The slice images are typically generated by Computerized Tomography (CT) or by Magnetic Resonance Imaging (MRI). Images may also be captured using Angiography, Single-Photon Emission Computed Tomography, and Positron Emission Tomography methods.
The images are typically stored and displayed in a series of static images on film. In addition, the images may be stored in a computer data-base and organized pursuant to a three dimensional coordinate system, which may be referred to as image space, such that each point in each of the images is identified by a unique coordinate.
The images can be used during the medical procedure to guide instruments or probes within the body of a patient. This means that smaller incisions into the body of the patient may be made during the procedure thereby decreasing the risk for the patient and the duration of the patient's hospital stay.
However, to effectively use the images during a procedure on the patient it is necessary to display the relative position and movement of the instruments and probes being used on the patient during the procedure with respect to the images contained in the data-base. In order to display the instruments and probes on the images, it is necessary to map or correlate the spatial position of the patient relative to the images stored in the data-base. This process of mapping the anatomical body of the patient with respect to the images is referred to as "registration".
Generally speaking, the registration procedure produces a one to one mapping between coordinates of the patient space and the corresponding coordinates of the image space. In this way, by knowing the coordinates of a feature in the patient space, the corresponding coordinates in the image space can be easily determined and the features can be displayed. Once this is accomplished, the position and movement of instruments and probes relative to the patient in the patient space can be displayed relative to the images in the image space.
The first step in the registration procedure is to identify at least three points, and preferably more, on the patient and then find the corresponding points in the images. Once these points in patient and image space have been correctly matched, it is possible to determine a rigid-body transformation to map the points in patient space onto the points in image space.
In the past, in order to perform this registration procedure, it had been necessary to manually correlate points on the patient with corresponding points in the images. This has been often done by identifying points on the patient in the patient space with a probe and, immediately thereafter, identifying the corresponding point in the image space. Another manner this had been done was by identifying points in a pre-determined order in the image space and then identifying the corresponding points on the patient in the same pre-determined order. In other words, the prior art devices required the user to manually correlate a set of points in the patient space with the corresponding points in the image space in order to perform the registration procedure.
The prior art has suffered from several disadvantages. In particular, it is inefficient and time consuming for a surgeon to identify specific points on a patient in a specific order and then locate and identify the corresponding points in the image. The difficulty is compounded when the number of points increases. Furthermore, an error in entering the points cannot be quickly identified and may require the recommencement of the registration procedure.
Accordingly, there has been a need in the art for an efficient and robust automated method and system to correlate points on an anatomical body with corresponding points in the image data-base so that a registration procedure can be performed. In addition, there is a need for a system which can accept points on the anatomical body and independently correlate the points with the selected points in the image data-base, regardless of the order or number of points on the anatomical body or data-base being selected.
Moreover, in order to accomplish this task, there is a need to overcome the inherent difficulty of correlating points on a spatial body with points on an image body when the points on both bodies are symmetrical about a plane, such as a plane centred down the face of a patient In other words, there is a need for a method and system which can discriminate between a true or correct match and a mirror image or symmetrically false match between points on the image and on the patient.